Congestive heart failure (CHF) is a condition that is often associated with a weakened heart that cannot pump enough blood to body organs. In CHF, the heart may be weakened due to hypertension, vascular disease, valvular disease, etc. Or, CHF may cause a fluid or chemical imbalance that leads to such diseases. In either case, once a patient is diagnosed with CHF, the disease typically worsens with time. CHF patients often have elevated heart rates, which may be considered a natural physiologic response to maintain or increase cardiac output. Cardiac output may be determined by multiplying stroke volume by heart rate. Hence an increase in heart rate may increase cardiac output. However, an increase in heart rate may be detrimental to a diseased heart. In particular, the condition of a diseased heart typically worsens in response to an increase in heart rate. Thus, to maintain or increase cardiac output, most agree that an increase in stroke volume is preferable to an increase in heart rate.
Traditional implantable pacing devices are often indicated for CHF patients. Such devices typically aim to compensate for CHF by maintaining a suitable heart rate; however, a controlled heart rate alone may do little to slow progression of CHF. Consequently, a need exists for methods and/or devices that can better address cardiac output issues, particularly in CHF patients. As discussed below, stimulation of parasympathetic nerves can help to address such cardiac output issues.